Vent construction for core boxes and the like and method of making same

ABSTRACT

A wall surface for venting air while confining particulate material of predetermined size, as for example sand. The construction has particular advantages as a vent for core boxes and comprises a thin flexible sheet having a plurality of small holes therein spaced more closely than the largest particle size of the particulate material to be retained. In the case of one type of sand for making foundry cores, the average sand particle size is approximately 0.025 inch and the largest particle size is approximately 0.034 inch. Holes spaced more closely than 0.034 inch cannot be plugged by at least the larger sand particles when adjacent to each other. The holes are conically shaped with the small diameter end of the openings facing the sand to be retained. Preferably the sheet is sufficiently thin and flexible that it will be bent by a blast of air from the reverse side to bow the foraminous strip and loosen the particles wedged in the inner small diameter end of the openings.

United States Patent [45] Patented Aug.3l,1971

[54] VENT CONSTRUCTION FOR CORE BOXES AND THE LIKE AND METHOD OF MAKING SAME 9 Claims, 6 Drawing Figs.

52 U.S.Cl 164/234, 164/410 5| 1nt.Cl B22c7/06 so FieldolSearch 164/234,

3,214,803 11/1965 Amt 164/234 X 2,669,769 2/1954 Peterson 164/120 X FOREIGN PATENTS 228,070 l/l925 Great Britain 164/234 Primary Examiner-J. Spencer Overholser Assistant Examiner-John S. Brown Attorney-William P. Hickey ABSTRACT: A wall surface for venting air while confining particulate material of predetermined size, as for example sand. The construction has particular advantages as a vent for core boxes and comprises a thin flexible sheet having a plurality of small holes therein spaced more closely than the largest particle size of the particulate material to be retained. In the case of one type of sand for making foundry cores, the average sand particle size is approximately 0.025 inch and the largest particle size is approximately 0.034 inch. Holes spaced more closely than 0.034 inch cannot be plugged by at least the larger sand particles when adjacent to each other. The holes are conically shaped with the small diameter end of the openings facing the sand to be retained. Preferably the sheet is sufficiently thin and flexible that it will be bent by a blast of air from the reverse side to bow the foraminous strip and loosen the particles wedged in the inner small diameter end of the openings.

BACKGROUND OF THE INVENTION In the founding art, cavities are produced in cast metals by means of sand temporarily held together by a binder to produce what is known as a core. The molten metal is poured around the core and is allowed to solidify. The binders used are temporary and can be decomposed, usually by prolong heat treatment and oxidation. The solidified metal having the core therein is subjected to conditions which decompose the binder, usually prolonged heating in air, following which the sand is shaken out of the cast metal body through one or more small openings.

The cores are produced in molds comprising two or more pieces (usually two) which can be disassembled to remove the core once the binder has hardened. The cores are produced by assembling the portions of the mold to provide an enclosure whose cavity corresponds in shape to the shape of the core desired. The cavity is filled with sand and binder, the binder is hardened, and the mold is disassembled to remove the finished core. In some instances the binder is a powder thatis mixed with the sand that is forced into the mold cavity. In other instances, the sand is coated with the binder and the coated sand is forced into the mold cavity. The sand and binder may be tamped into the mold cavity, but in the process with which I am concerned, the sand is blown into the mold cavity by means of compressed air. The air displaced by the sand as well as any compressed air reaching the cavity must be vented therefrom in order to be sure that no air pockets or soft spots exist in the finished cores. The air is vented through screening devices commonly called vents which retain the sand and binder while allowing the escape of the air. These vents are subject to sand abrasion, which can be quite severs in those instances where some of the sand particles are forced through the openings ofthe vent. In all prior art vents with which I am concerned, sand and binder tends to accumulate in the air passages of the vent. Sand particles just slightly larger than the openings through the vent become wedged in the opening, and this wedging process continues until substantially all of the openings through the vent become plugged. Most molds are designed with only sufficient venting capacity to make satisfactory molds when the vents are in an unplugged condition, and consequently the quality of the cores deteriorate when the vents start to become plugged. in many instances the core producing process is carried on in automatic machinery and the plugged condition of the vents is not ascertained until a sizable production of nonusable cores has been produced.

Air blown cores are made by a number of different processes. In one commonly used process, an oil such as linseed oil is used to coat the sand which is air blown into the molds. The unhardened cores made with the oxidizing oil is removed and placed in dryers which allows air circulation therethrough. The dryers containing the cores are put in ovens where oxidization of the binder takes place to set the binder to a rigid condition. This is sometimes called a green sand molding process.

Another type of process commonly used is called the hot box process In the hot box process, sand is either coated with or mixed with a thermosetting resin, (usually a phenolformaldehyde) and is air blown into the cavity of the mold. The mold is heated, and after the resin and sand has become stationary against the mold cavity surface for a few seconds, the resin is transformed into its thermoset condition, and thereafter the mold is split and the core removed from the mold cavity. Other types of thermosetting resins can be used, as for example phenol-furfural resins, etc.

Air blown cores can also be made by several cold processes wherein a gas is caused to pass through the core to set up the binder after the sand and binder are blown into the mold cavity. In one such process, sand is coated with a sodium silicate binder and this binder coated sand is then blown into the mold cavity. Thereafter, carbon dioxide is caused to flow through the core to gel the sodium silicate. In order that properly uniform hard cores are made, the carbon dioxide must reach all parts of the core and must displace the air in the pores between the sand particles. In this process it is particularly necessary that the vents remain open and in an unplugged condition, otherwise the air in some portions of the core is not displaced with the carbon dioxide, and a soft core results.

In another type of cold core making process, sand and an oil containing a polyalcohol, such as a glycol, is air blown into the mold cavity. Thereafter a diisocyanate, as for example methylene bis (phenylene isocyanate) or 2,4-toluenediisocyanate is blown through the pores of the core to set the binder. oil into a cross-linked condition. Here again the openings of the vents must be kept open if soft cores are to be avoided.

Still other cold methods of making cores involving blowing gases through the sand and binder have been, and will be developed, and in all of these processes it is critical that the passages through the vents remain open.

An object of the present invention is the provision of a new and improved foraminous sheet for core box vents and the like which will retain particles of a predetermined particle size in a manner assuring that a certain percentage of the openings will remain open.

Another object of the present invention is the provision of a new and improved foraminous vent sheet of the above described type having a plurality of holes therethrough from which embedded sand particles can be easily removed.

Further objects and advantages of the invention will become apparent to those skilled in the art to which the invention relates from the following description of several preferred embodiments.

SUMMARY OF THE INVENTION According to the invention, a vent for separating granular material from a fluid and in particular a vent for a core box and I the like is formed by a thin plate having holes therethrough of a size less than the smallest size to be retained and a spacing that is less than the largest particle size to be retained. The-openings through the sheet are conically shaped with the smallest cross section of the opening being positioned at the surface to be engaged by the granular material and the largest cross section of the opening positioned at the opposite face of the sheet. The sheet is flexible so that it can be flexed in the reverse direction to the venting air flow to loosen particles which may become lodged in the small end of the openings, and the sheet is preferably thinner than the average particle size to be retained.

The advantages of the invention can best be understood from the description of the operation of a core box wherein at least a portion of the walls of the core molding cavity is formed by the above described sheet. The air that is displaced from the cavity by the sand blown into the cavity passes outwardly through the above described openings. Small particles of binder, which may be present in a loose condition, and which are less than the minimum size of the openings, will pass through the openings along with the vented air. Small particles of sand will become lodged in some of the openings during the core molding process, but because of the size and spacing of the holes, a sizable percentage of the holes cannot become plugged in any one core molding operation. Because particles of the largest size are randomly distributed, it will always happen that a certain percentage of the vent area will be engaged by adjacent sand particles of the largest particle size being used. Because the openings are more closely spaced than is the spacing of adjacent large size particles, it is impossible for one of two adjacent large size particles to fit into a hole when the other adjacent large size particle is seated in a hole. A passage, therefore, is assured through the opening beneath the large size particle that is supported by the plate above the opening, and this condition will occur in a certain percentage of the openings, generally randomly distributed throughout the surface of the sheet. The result is that even though a sizable percentage of the openings are plugged at any one core making operation, a sizable percentage cannot be plugged, and because the sheet material covers a large area of the mold, adequate venting area is provided. Not only is adequate venting area provided, but the venting area is distributed over a much greater area than is provided by conventional core vents, so that a core of more uniform density is produced using the present invention.

The core mold will preferably have a venting area which extends completely around one section of the core molding cavity and in some instances the entire sidewalls of the cavity can be made of the venting material of the present invention. Because the invention makes it convenient to provide a venting over appreciable areas, area venting can be built into the core molds and in doing so a more uniform venting is accomplished. Because the venting area is made from a sheet which is thin and flexible, it can be flexed inwardly after the finished core is removed from the mold to dislodge sand particles that may be embedded in the small diameter end of the openings. This flexing is conveniently accomplished by a blast of high pressure air counter current to the normal venting flow. Also, because the sheet has a thickness less than the maximum particle size of the sand and preferably less than the average particle size of the sand, a flat tool can be drawn over the back side of the sheet to engage particles projecting therefrom and thereby force them out of the holes into the core making cavity of the mold.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view through an assembled core box, blow plate and sand reservoir and depicts the process of air blowing a core in a core box embodying principals of the present invention;

FIG. 2 is a fragmentary sectional view of the vent material shown in FIG. 1; 1

FIG. 3 is a schematic sectional view, similar to FIG. 1, but showing another embodiment of core box;

FIG. 4 is a plan view of a tubular core box vent having one end of the foraminous vent material of the present invention;

FIG. 5 is a sectional view taken on line 5-5 of FIG. 4; and

FIG. 6 is aschematic sectional view depicting a preferred method of making the vent material of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A One of the principal uses of the present invention is in the venting of sand core producing molds and the like, during the core blowing of forming process. In the process of blowing cores depicted in FIG. 1, a mixture of sand and resin 10 is blown from a pressure reservoir 12 through an orifice 14 in a blow plate 16 into the cavity 18 of a core mold 20. The air that is displaced from the cavity 18 by the sand and binder exits through a vent 22 embodying principals of the present invention. In the embodiment shown in FIG. 1, the vent 22 is formed by an annular band or ring of stainless steel sheet material having small holes therethrough made in accordance with the principals above described. In the embodiment shown, the sheet material is made from 0.015 inch stainless steel stock and has tapered openings therethrough having a diameter of 0.012 inch facing the cavity 18, and 0.016 inch facing outwardly of the cavity. These openings are spaced 0.022 inch apart on 60triangular centers. A typical sand which is used with the above described vents has sand particles ranging from approximately 0.012 inch to approximately 0.034 inch.

The mold shown in FIG. 1 has a top ring portion 26 that is supported in space relation from the remainder 28 of the mold 20 by support straps 30 which bridges the annular clearance or opening 32. The top ends of the support straps 30 are welded to the top ring 26, and the bottom ends of the support straps 30 are welded to the bottom portion 28 of the mold 20. The adjacent inside edges of the ring 26 and bottom portion 28 are recessed as at 34 and 36 respectively'to a depth just equal to the thickness of the vent strip 22, and the vent strip is seated therein with its inside surface flush with the remaining inside surface of the cavity 18. I

It will be seen that the sand that is used has a particle size which varies, usually over a range that is approximately less than 4 diameters. The generally randomed distribution of these particles will cause a certain percentage of the largest diameter particles to be adjacent each other when they engage the surface of the vent 22. Because the center to center dimension of the engaging large size particles is greater than the center to center spacing of the holes, it is impossible for adjacent large size particles to plug off more than one of the two openings therebeneath. The unplugged opening assures venting in this area of the core, and these unplugged openings will be randomly distributed over the surface of the vent 22. The air that is vented, of course, passes through the annular space 32 to the surrounding atmosphere.

During the core forming process, some of the sand particles will embed themselves in the inner ends of the holes 38 in the vents 22. Some of the sand particles which are lodged in the openings 38 will be attached to the remainder of the core by the binder, such that they will be pulled from the openings when the core is removed. Some of the sand particles may remain lodged in the openings of the vent 22, however, and after several cores are made, and sometimes after every core is made, a blast of air from a high pressure nozzle or nozzles 40 is caused to pass through the opening 32 and impinge upon the back side of the vent 22. The air blast from the nozzles bows the vent strip inwardly to stretch the metal around the inner ends of the openings and loosen the particles lodged therein. The blast of air simultaneously exerts a force on the sand particles to remove them from the openings. If it should occur that this procedure does not loosen all of the sand from the openings, a tool can be inserted through the opening 32 to bear against the backside of the strip 24. Because the strip has a thickness less than approximately that of the smallest size particles, and because the openings are close to the diameter of the smallest size particles, some of the particles lodged in the openings will project through the openings and these can be engaged by the surfaces of a tool rubbed across the back surface of the vent strip 24.

A cross section of the vent material of the present invention is shown in FIG. 2. It will be seen that the openings 38 are tapered with the small diameter ends all adjacent one side of the vent and the large diameter ends all adjacent the other side of the vent. The small diameter end of the holes 38 have a diameter equal to or just slightly less than the thickness of the plate, and this diameter is less than the smallest size of the sand which is to be retained. Sand particles, if perfect spheres, when lodged in the openings may or may not project through the openings depending on the thickness of the sheet. Round particles that do not project through the openings will not be embedded tightly in the openings and can easily be removed by air pressure. Oblong shaped particles however, tend to become more tightly embedded in the openings because of the shallow angle of engagement with the small diameter end of the openings, and when such are embedded in the openings, they will project through the strip material 24. These oblong particles may not be removed by a blast of air but their projecting ends can be engaged by a tool. If oblong particles lay flatwise over the openings, they will not become embedded in the openings. It will therefore be seen that adequate venting capacity is assured during any single core forming operation provided that the operation is started with a clean screen. It will further be seen that the construction of the vent sheet is such that any particle of the sand which becomes lodged therein can be removed either with a blast of high pressure fluid, or if necessary by the engagement of a tool from the backside of the vent.

The embodiment shown in FIG. 3 of the drawings is generally similar to that shown in FIG. 1 and differs principally therefrom in that all of the cavity forming surfaces of the core mold, not engaged by the core plate, are made from the venting strip material of the present invention. Those portions of the embodiment shown in FIG. 3 which correspond to similar portions of the embodiment shown in FIG. 1 are designated by a like reference numeral characterized further in that a suffix a is afiixed thereto.

The mold 200 is formed in two half sections, each half section of which forms a semicylinder which is closed otf at one end by a semicircular end wall. The end wall is welded or otherwise secured to the semicylindrical section, and the mold is completed by a split angle rim at the top, and welded angle stiffeners 44 which extend down the sides and across the bottom of the mold. The mold a is operated in the same manner as is the mold 20, and can be cleaned in the manner as described above.

Although the sheet material of the present invention has the advantage that it can be used to cover large mold cavity areas, it can also be used as the surfacing for conventional tubular vents as shown in FIGS. 4 and 5. A tubular body 46 is provided with an internal counterbore 48 at one end to form a shoulder 50. A circular disk 52 of the sheet material of the invention is seated on the shoulder 50 and the outer end 54 of the sidewalls is rolled over to hold the disk in place. The vent is used by pressing it in an opening of a core mold with the disk 52 generally coterminous with the internal surfaces of the mold cavity.

The vent material described above contains holes which are so small and which are spaced so closely together that it cannot be made economically by drilling or stamping sheet material. According to the preferred method of making the vent of the present invention, a sheet of metal is acid etched by the process shown schematically in FIG. 6. In the process shown in FIG. 6 a photographic resist material 60 is applied as a coating to the top and bottom surfaces of a thin metal sheet, and the bottom surface of the coated strip is exposed to a light through a photographic film having light transmitting portions corresponding with the holes desired. The light struck resist material is then developed to remove the coating in the light struck areas. The holes 62 in the resist material have a diameter of 0.008 inch and are spaced 0.022 inches apart on triangular centers. The plate is supported with the holes 62 on the bottom over an acid spray shown in FIG. 6 as issuing from a plurality of nozzles 64. The acid penetrates the holes 62 and eats out the metal of the sheet material 24. Because the openings 62 are in only one surface of the resist coating .60, the metal is eaten away from one side only of the sheet to produce openings when finished having a diameter of 0.0l6 inch adjacent the openings 62 and a diameter of 0.012 inch at the top surface of the sheet 24. It will be apparent that the process can be carried out to make strips of any size, by moving a small size negative after each exposure until all of the resist material is exposed. It will further be seen that the holes in the negative need not be uniform throughout its entire area, and that the holes can be arranged in various patterns including that of letters, or numbers to form words 09 groups of numbers.

While the invention has been described in considerable detail,.l do not wish to be limited to the particular embodiments shown and described, and it is my intention to cover hereby all novel adaptations, modifications, and arrangements thereof which come within the practice of those skilled in the art to which the invention relates.

I claim:

1. A core box and the like for retaining particulate material of less than a predetermined particle size of approximately 0.034 inch, comprising: a container having a internal cavity the sidewalls of at least a portion of which is formed by sheet material having a thickness less than said predetermined size, said sheet material having holes therethrough of circular cross section of less than said predetermined size of approximately 0.034 inch facing said cavity and spaced no greater than a distance enerall equal to said predetermined size of approximately 0. 34 inc sard holes having a conical surface with the smaller diameter end of said openings being positioned adjacent'said internal cavity, and means for introducing said particulate material to said cavity to displace fluid through said openings.

2. A core box and the like for retaining a small particulate material, such as foundry sand, having upper and lower limits of particle size of approximately 0.034 and 0.012 inch respectively with an average size in between the limits, comprising: a container having an internal cavity the sidewalls of at least a portion of which is formed by sheet material having a thickness less than said average size, said sheet material having holes therethrough of circular cross section of less than said lower limit of 0.012 inch facing said cavity and spaced no greater than a distance generally equal to said upper limit of 0.034 inch, said holes having a conical surface with the smaller diameter end of said openings being positioned adjacent said internal cavity, and means for introducing said particulate material to said cavity to displace fluid through said openings.

3. The core box of claim 2 wherein said holes are spaced apart in a triangular pattern.

4. The core box of claim 3 wherein said sheet is sufficiently flexible to be flexed by air pressure.

5. The core box of claim 3 wherein said sheet forms at least one continuous circumferential portion of said cavity.

6. The core box of claim 2, wherein said sheet is approximately 0.015 inch thick and said holes are circular in section with a diameter approximately 0.012 inch at one surface and approximately 0.016 inch at the other surface.

7. The core box of claim 6 wherein said holes are spaced on approximately 0.022 inch centers in approximately a 60 pattern.

8. The core box of claim 7 wherein the sheet material is stainless steel.

9. The core box of claim 2 wherein the major portion of the sidewalls of said cavity are formed by said sheet material. 

1. A core box and the like for retaining particulate material of less than a predetermined particle size of approximately 0.034 inch, comprising: a container having a internal cavity the sidewalls of at least a portion of which is formed by sheet material having a thickness less than said predetermined size, said sheet material having holes therethrough of circular cross section of less than said predetermined size of approximately 0.034 inch facing said cavity and spaced no greater than a distance generally equal to said predetermined size of approximately 0.034 inch, said holes having a conical surface with the smaller diameter end of said openings being positioned adjacent said internal cavity, and means for introducing said particulate material to said cavity to displace fluid through said openings.
 2. A core box and the like for retaining a small particulate material, such as foundry sand, having upper and lower limits of particle size of approximately 0.034 and 0.012 inch respectively with an average size in between the limits, comprising: a container having an internal cavity the sidewalls of at least a portion of which is formed by sheet material having a thickness less than said average size, said sheet material having holes therethrough of circular cross section of less than said lower limit of 0.012 inch facing said cavity and spaced no greater than a distance generally equal to said upper limit of 0.034 inch, said holes having a conical surface with the smaller diameter end of said openings being positioned adjacent said internal cavity, and means for introducing said particulate material to said cavity to displace fluid through said openings.
 3. The core box of claim 2 wherein said holes are spaced apart in a triangular pattern.
 4. The core box of claim 3 wherein said sheet is sufficiently flexible to be flexed by air pressure.
 5. The core box of claim 3 wherein said sheet forms at least one continuous circumferential portion of said cavity.
 6. The core box of claim 2, wherein said sheet is approximately 0.015 inch thick and said holes are circular in section with a diameter approximately 0.012 inch at one surface and approximately 0.016 inch at the other surface.
 7. The core box of claim 6 wherein said holes are spaced on approximately 0.022 inch centers in approximately a 60* pattern.
 8. The core box of claim 7 wherein the sheet material is stainless steel.
 9. The core box of claim 2 wherein the major portion of the sidewalls of said cavity are formed by said sheet material. 